我是否发现了 libxml2 bug（多线程解析中的内存泄漏）？

Question

我实际上正在使用 libxml2 编写数据处理代码。我陷入了无法消除的内存泄漏。下面是生成它的最小代码：

#include <stdlib.h>
#include <stdio.h>
#include <libxml/parser.h>
#include <libxml/tree.h>
#include <omp.h>

int main(void)
{
    xmlDoc *doc;
    int tn;
    char fname[32];

    omp_set_num_threads(2);
    xmlInitParser();
    #pragma omp parallel private(doc,tn,fname)
    {
        tn  = omp_get_thread_num();
        sprintf(fname,"testdoc%d.xml",tn);
        doc = xmlReadFile(fname,NULL,0);
        printf("document %s parsed on thread %d (%p)\n",fname,tn,doc);
        xmlFreeDoc(doc);
    }
    xmlCleanupParser();

    return EXIT_SUCCESS;
}

在运行时，输出是：

document testdoc0.xml parsed on thread 0 (0x1005413a0)
document testdoc1.xml parsed on thread 1 (0x1005543c0)

确认我们确实具有多线程，并且 doc 在并行区域中确实是私有的。人们可以注意到，我正确应用了使用 libxml2 的线程安全指令（http://xmlsoft.org/threads.html< /a>）。 Valgrind 报告：

HEAP SUMMARY:
    in use at exit: 9,000 bytes in 8 blocks
  total heap usage: 956 allocs, 948 frees, 184,464 bytes allocated

968 bytes in 1 blocks are definitely lost in loss record 6 of 8
   at 0x1000107AF: malloc (vg_replace_malloc.c:236)
   by 0x1000B2590: xmlGetGlobalState (in /opt/local/lib/libxml2.2.dylib)
   by 0x1000B1A18: __xmlDefaultSAXHandler (in /opt/local/lib/libxml2.2.dylib)
   by 0x100106D18: xmlDefaultSAXHandlerInit (in /opt/local/lib/libxml2.2.dylib)
   by 0x100041BE7: xmlInitParserCtxt (in /opt/local/lib/libxml2.2.dylib)
   by 0x100042145: xmlNewParserCtxt (in /opt/local/lib/libxml2.2.dylib)
   by 0x10004615E: xmlCreateURLParserCtxt (in /opt/local/lib/libxml2.2.dylib)
   by 0x10005B56B: xmlReadFile (in /opt/local/lib/libxml2.2.dylib)
   by 0x100000E03: main.omp_fn.0 (in ./xtest)
   by 0x100028FA3: gomp_thread_start (in /opt/local/lib/gcc44/libgomp.1.dylib)
   by 0x1001E8535: _pthread_start (in /usr/lib/libSystem.B.dylib)
   by 0x1001E83E8: thread_start (in /usr/lib/libSystem.B.dylib)

LEAK SUMMARY:
   definitely lost: 968 bytes in 1 blocks
   indirectly lost: 0 bytes in 0 blocks
     possibly lost: 0 bytes in 0 blocks
   still reachable: 8,032 bytes in 7 blocks
        suppressed: 0 bytes in 0 blocks
Reachable blocks (those to which a pointer was found) are not shown.
To see them, rerun with: --leak-check=full --show-reachable=yes

无论使用什么 XML 文档，这都对我有用。我在 Mac OS X 10.6.5 上使用 libxml 2.7.8 和 gcc 4.4.5。

有人能够重现这个错误吗？

谢谢，

安东尼

Answer 1

从上面列出的网站 (http://xmlsoft.org/threads.html)：

从 2.4.7 开始，libxml2 做出了规定，以确保并发线程可以安全地并行解析不同文档。

您的示例似乎对每个线程的同一文档（testdoc.xml）使用 xmlReadFile。它进一步指出：

注意，多个线程共享同一个文档无法保证线程安全，必须在应用程序级别进行锁定...

Answer 2

您可能应该在 libxml2 邮件列表中提出这个问题。

http://mail.gnome.org/mailman/listinfo/xml